Association between fish consumption, long chain omega 3 fatty acids, and risk of cerebrovascular disease: systematic review and meta-analysis

Abstract

Objective: To clarify associations of fish consumption and long chain omega 3 fatty acids with risk of cerebrovascular disease for primary and secondary prevention.

Design: Systematic review and meta-analysis.

Data sources: Studies published before September 2012 identified through electronic searches using Medline, Embase, BIOSIS, and Science Citation Index databases.

Eligibility criteria: Prospective cohort studies and randomised controlled trials reporting on associations of fish consumption and long chain omega 3 fatty acids (based on dietary self report), omega 3 fatty acids biomarkers, or supplementations with cerebrovascular disease (defined as any fatal or non-fatal ischaemic stroke, haemorrhagic stroke, cerebrovascular accident, or transient ischaemic attack). Both primary and secondary prevention studies (comprising participants with or without cardiovascular disease at baseline) were eligible.

Results: 26 prospective cohort studies and 12 randomised controlled trials with aggregate data on 794,000 non-overlapping people and 34,817 cerebrovascular outcomes were included. In cohort studies comparing categories of fish intake the pooled relative risk for cerebrovascular disease for 2-4 servings a week versus ≤ 1 servings a week was 0.94 (95% confidence intervals 0.90 to 0.98) and for ≥ 5 servings a week versus 1 serving a week was 0.88 (0.81 to 0.96). The relative risk for cerebrovascular disease comparing the top thirds of baseline long chain omega 3 fatty acids with the bottom thirds for circulating biomarkers was 1.04 (0.90 to 1.20) and for dietary exposures was 0.90 (0.80 to 1.01). In the randomised controlled trials the relative risk for cerebrovascular disease in the long chain omega 3 supplement compared with the control group in primary prevention trials was 0.98 (0.89 to 1.08) and in secondary prevention trials was 1.17 (0.99 to 1.38). For fish or omega 3 fatty acids the estimates for ischaemic and haemorrhagic cerebrovascular events were broadly similar. Evidence was lacking of heterogeneity and publication bias across studies or within subgroups.

Conclusions: Available observational data indicate moderate, inverse associations of fish consumption and long chain omega 3 fatty acids with cerebrovascular risk. Long chain omega 3 fatty acids measured as circulating biomarkers in observational studies or supplements in primary and secondary prevention trials were not associated with cerebrovascular disease. The beneficial effect of fish intake on cerebrovascular risk is likely to be mediated through the interplay of a wide range of nutrients abundant in fish.

Fig 1 Flow of studies in review

Fig 2 Association between fish consumption and risk of cerebrovascular disease in prospective cohort studies with information on intake categories and weekly increment of servings

Fig 3 Association of long chain omega 3 fatty acids and fish consumption with cerebrovascular disease, based on prospective cohort studies, comparing risk in top versus bottom third of baseline levels. *To allow consistent indirect comparison, includes prospective cohort studies with available risk estimates comparing top versus bottom thirds of fish consumption

Fig 4 Effects of long chain omega 3 fatty acid supplementations on cerebrovascular disease, derived from randomised control trials. *Trials involving participants with no pre-existing cardiovascular disease at baseline. †Trials including participants with previous or existing cardiovascular disease at baseline. ‡Based on studies with available information on subtype